Mari, 29, was among six people attacked while shopping with his family at the Assago shopping centre in the Italian city of Milan.
He is currently on loan at Serie A side Monza.
Mari was taken to hospital after the attack, where he is understood to be conscious and not in a serious condition.
He is expected to have surgery to reduce muscle damage to his back.
The club’s chief executive Adriano Galliani was quoted by Sky Sports Italy as saying: “Pablo Mari had a fairly deep wound on his back, which fortunately did not touch vital organs such as the lungs or other.
“His life is not in danger, he should recover quickly.”
